In 2010, we have advanced the objectives of this project as follows:It is well known that multiple serial passages of a wild-type virulent virus in cell culture often results in the loss of virulence of the virus in a homologous host, which has been a traditional strategy in generating attenuated live viral vaccines including Rotarix vaccine. However, mechanisms underlying this phenomenon are not well understood. In 2009, by sequencing the whole genome of an avirulent murine rotavirus passaged multiple times serially in mouse pups and a virulent murine rotavirus passaged multiple times serially in cell cultures, we reported that at least two genes encoding VP4 and NSP4, respectively, were involved independently in murine rotavirus pathogenesis in mice. To gain insight into host-induced genomic mutations of rotavirus, we passaged a human diarrheal stool suspension containing G1P8 virus (four strains), G8P4 virus (one strain) or G9P8 virus (one strain) serially up to 40 times in two different cell cultures (primary AGMK cells and human colon adenocarcinoma cell line HT29). The whole genome sequence of six virulent virus strains in stool samples as well as 12 cell culture-passaged virus strains (6 in primary AGMK cells and 6 in HT29 cells) was determined. Analyses of the sequences obtained are in progress. Preliminary sequence analyses suggested that (i) the integrin binding site on the VP4 protein;(ii) glycosylation of the VP7 protein;and (iii) NSP4 protein were involved in rotavirus virulence/avirulence.